Much of our current understanding of cardiac biology and function is derived from isolated heart preparations, whole organ level imaging, in vitro model systems and/or static endpoint analyses. In order to uncover fundamental biological principles and ultimately improve the treatment of cardiac diseases, new approaches for in vivo cellular level imaging in the beating heart are needed. We have recently developed such new technology (Nature Commun 2012;3:1054) employing a unique stabilizer setup, gating algorithm and new imaging reporters. This technological advance has allowed us to quantitate the contractile cycle of single cardiomyocytes, recruitment of host cells during complex healing mechanism following infarction (Nature 2012;487:325-9; Science 2013;339, 161-6) and drug action at the single cell level (Nature Commun 2013;4:1504). The goal of this application is to advance this cutting-edge in vivo imaging technology and to apply it to quantitative measurements of pharmacological intervention in the heart. Namely, we will develop and validate cardiac response markers, synthesize and test putative cardioprotective drugs and develop quantitative algorithms for image analysis. We anticipate that the new technology will have considerable applications in expanding our understanding of cardiac biology, and ultimately clinically translatable therapeutic intervention.